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Old 02-27-2011, 11:39 PM   #151 (permalink)
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The double one is the older template, and the one with the angle numbers is the newer.

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Old 02-28-2011, 06:38 AM   #152 (permalink)
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OK, thanks AeroModder!!

I will have to try and get some good level/squared up pics so I can see what I need to do. My truck has a very short bed on it. So, I don't think it'll slope too much if I can possibly make a cover for it. I might be able to reuse the frame from the soft bed cover I have now.
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Old 02-28-2011, 12:52 PM   #153 (permalink)
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LUVMY02CREW -

Here's a nice image of your truck to work with :



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Old 02-28-2011, 05:55 PM   #154 (permalink)
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Prius

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Originally Posted by AeroModder View Post
While doing some overlay work, I've noticed that the template is actually tilted slightly. The base isn't quite level. The base of the template is tilting up at the rear by about .6 degrees, according to GIMP's measure tool.

Here's the rotated image:



I found the tilt when overlaying the template to a 3rd gen Prius, since I'm using it as inspiration for my Aspire project. I'm thinking if the Prius goes a bit steeper than the template and still manages good flow, maybe I can get away with something similar.

The image of the Prius wasn't level either, but I tweaked the images to work. I didn't make it level, since it was making it look distorted.

One of the members recently posted an article about the Prius in which the designer spoke of the cars shape being close to the ideal.
Due to General Motors' designers past comments about
'outward vision' requirements I think the rooflines are intentionally a bit 'fast' so as to improve vision through the backlite.And I'm okay with that.
If you get anywhere reasonably near the template I think you'll be rewarded at the pump.
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Old 02-28-2011, 06:02 PM   #155 (permalink)
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Cd 0.186

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Originally Posted by NeilBlanchard View Post
Here's an interesting comparison:

Neil,Hucho tested the Schl'o'r car at VW's tunnel and got Cd 0.186.It has amazing plan-taper when viewed from overhead.If they'd done basjoos movable front skirts they could have seriously reduced frontal area,a big criticism of Hucho.
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Old 02-28-2011, 06:12 PM   #156 (permalink)
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either

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Originally Posted by LUVMY02CREW View Post
AeroModder
- Just to be sure I'm not confused, would you please clarify what you meant by "The newer template is edited"...was it the double template that I reposted or another one that I missed????
- AND thanks about the "GIMP" software, I looked into that a bit earlier and that might be the way I go...free stuff is great

cfg83
- I agree that it would be helpful if aerohead and the mods could update and clarify which to use. Everyone "reading off the same page" can only be a good thing in the long run.
Either of the templates can be used.The newer one is 'cleaner' and has some 'boundaries' established for under vehicle mods so nothing will get knocked off on a driveway ramp,railroad crossing,etc..
The curvature down the roofline is the most critical part as far as streamlining as it will prevent separation.And this goes for the sides as well.
If you can do the plan taper as well as the roof curvature you'll pick up a little extra drag reduction.
Just find the location along the side of the vehicle where it is widest and do the best-fit for what you have.If there is no body camber at all,you just have to start at zero and work back.
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Old 05-18-2011, 12:07 PM   #157 (permalink)
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Aerohead I have a question for you if I may. Looking at the shape of the template discussed, it's easy to see how this shape will create minimal drag. What I'm working with is a 25 foot class C motor home with the typical square box rear end, which presumably creates huge amounts of drag.

I'm going to build a cone for the rear to see what effect it has. The height of this vehicle makes following the lines of the discussed shape impossible to follow without making the cone as long, or longer than the body, which is not practical. Can you give me an educated guess of what shape might be the best compromise for the 'square' rear end of this type of shape, or do you think the compromised resulting shape would be worth the effort?
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Old 05-18-2011, 12:32 PM   #158 (permalink)
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Here is a van that has had some significant work done in terms of aero-improvements. It should compare to your motor home quite well.
They start with a van, and make it very blocky, then do the aero. It is all done by NASA Dryden Flight Research Center, and they drop from CD=0.89 (blocky) to 0.238 (rounded nose and full boat tail). This is not a practical van for daily driving, but it's neat to look at and get inspiration from. It's ALL the way at the bottom, and it's in French, but you should be able to click on pictures for better quality, and it should be easy enough to understand. You can also download the report (from Dryden in English) where it has all bold writing. You may also notice that the difference between their truncated boat tail and full boat tail realized little to no difference. Don't be discouraged by this, because when you look at the pictures of flow patterns on the full boat tail, you will notice that almost everything past the truncation is detached flow anyway.
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Old 05-18-2011, 01:16 PM   #159 (permalink)
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That is fabulous information Wyatt, thank you very much. I am inspired to carry on with this project. That curved four-sided approach is exactly what I thought might be the best shape for back there. The last few feet of the tip not making that much a difference is also encouraging

Judging roughly by the photos, the rear truncated cone is about 23% of the length of the modified vehicle shape. That means to be somewhat proportional, my rear cone would be about 6 long, that's totally doable. I was thinking more like 10 feet since the box is so big.

The drag reduction numbers for this project are staggering. Square at both ends, .89CD, fully rounded front, truncated rear cone, full belly pan, .242CD. That's only a 72.8% reduction in drag!! Wow. Now I just have to figure out what materials to use to build the cone. Thanks again, great information. Yea, NASA!
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Old 05-18-2011, 06:34 PM   #160 (permalink)
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RVs

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Originally Posted by orbywan View Post
That is fabulous information Wyatt, thank you very much. I am inspired to carry on with this project. That curved four-sided approach is exactly what I thought might be the best shape for back there. The last few feet of the tip not making that much a difference is also encouraging

Judging roughly by the photos, the rear truncated cone is about 23% of the length of the modified vehicle shape. That means to be somewhat proportional, my rear cone would be about 6 long, that's totally doable. I was thinking more like 10 feet since the box is so big.

The drag reduction numbers for this project are staggering. Square at both ends, .89CD, fully rounded front, truncated rear cone, full belly pan, .242CD. That's only a 72.8% reduction in drag!! Wow. Now I just have to figure out what materials to use to build the cone. Thanks again, great information. Yea, NASA!
orbywan,in the 1960s some of the lowest drag semi-trailer setups were ones in which most of the air was shunted around the rig,not over it.
Since these vehicles are taller than they are wide they are in a world of their own,aerodynamically.
One might just take the width to be the parameter for design.That said,one could multiply the width by 1.78 and this would be the theoretical distance behind the vehicle at which a boat-tail would come to a point.This would be 100% 'Template.'
It's only an assumption.
GM's 'OPTIMUM' boat-tail,at Texas Tech was about 5.5 feet long,for an 18-wheeler with 8-foot wide trailer van.It was just chopped off like a loaf of bread,as Breer,Fachsenfeld,Kamm,and others had done.


Last edited by aerohead; 05-18-2011 at 06:36 PM.. Reason: add data
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